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General Genetics (Practical Session) BIO221 Lecturer Alshehri, Dokhnah Saeed [email protected] Alshehri, Dikhnah Saeed THE TH 9 LAB The Structure of the DNA and RNA Alshehri, Dikhnah Saeed OUTLINES: The structure of DNA and RNA. DNA and RNA are polynucleotides. The rule of getting complementary base pairing Some practical exercise And class activates. Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed Genetic material of living organisms is either DNA or RNA. DNA – Deoxyribonucleic acid RNA – Ribonucleic acid Genes are lengths of DNA that code for particular proteins. Alshehri, Dikhnah Saeed Both DNA and RNA are polynucleotides. They are made up of smaller molecules called nucleotides. DNA is made of two polynucleotide strands: Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide Nucleotide RNA is made of a single polynucleotide strand: Nucleotide Alshehri, Dikhnah Saeed Nucleotide Nucleotide Nucleotide Nucleotide A nucleotide is made of 3 components: A Pentose sugar This is a 5 carbon sugar The sugar in DNA is deoxyribose. The sugar in RNA is ribose. Alshehri, Dikhnah Saeed A Nitogenous base In DNA the four bases are: Thymine Adenine Cytosine Guanine In RNA the four bases are: Uracil Adenine Cytosine Guanine Alshehri, Dikhnah Saeed Pyramidines Purines Thymine - T Adenine - A Cytosine - C Guanine - G Uracil - U Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed Nucleotides are connected to each other via the phosphate on one nucleotide and the sugar on the next nucleotide A Polynucleotide Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed The Nitrogenous Bases pair up with other bases. For example the bases of one strand of DNA base pair with the bases on the opposite strand of the DNA. Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed THE RULE: Adenine always base pairs with Thymine (or Uracil if RNA) Cytosine always base pairs with Guanine. This is beacuse there is exactly enough room for one purine and one pyramide base between the two polynucleotide strands of DNA. Nucleic Acid Nucleobases DNA adenine(A), thymine(T), guanine(G), cytosine(C) A=T , G≡C RNA adenine(A), uracil(U), guanine(G), cytosine(C) A=U , G≡C Alshehri, Dikhnah Saeed Base complement Purines Pyramidines Adenine Thymine Adenine Uracil Guanine Cytosine Alshehri, Dikhnah Saeed Property 1 - it must contain, in a stable form, information encoding the organism’s structure, function, development and reproduction Property 2 - it must replicate accurately so progeny cells have the same genetic makeup Property 3 - it must be capable of some variation (mutation) to permit evolution Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed EXERCISE 1 One strand of DNA has the base sequence: CGATTGGCAGTCAT Determine the sequence of bases in the complementary strand of mRNA that would form next to this DNA strand. Write the sequence of bases in the complementary mRNA strand. Alshehri, Dikhnah Saeed THE ANSWER: C always pairs with G, and A always pairs with T. However since this is mRNA and all RNA uses Uracil instead of Thymine. A will pair with U. GCUAACCGUCAGUA Alshehri, Dikhnah Saeed EXERCISE 2 Write the complementary strand of DNA to the following sequence. 5′ A-C-T-C-G-G-T-A-A 3′ Alshehri, Dikhnah Saeed THE ANSWER: Remember, A pairs with T and G pairs with C. Go through the original 5′ to 3′ sequence pairing each A with T and each C with G. Keep in mind that the complementary strand will read from left to right in the 3′ to 5′ direction. Therefore, the complementary strand starts with 3’ and ends with 5’. Original strand 5′ A-C-T-C-G-G-T-A-A 3′ The Complementary 3′ T-G-A-G-C-C-A-T-T 5′ Alshehri, Dikhnah Saeed EXERCISE 3 What is the DNA template that codes for the mRNA segment with the nucleotide sequence of sequence of 5′ G-C-U-A-G-U 3′ ? Alshehri, Dikhnah Saeed THE ANSWER: Again, there are two ways to approach this problem: Memorizing base-pair rules: Complementary bases in mRNA 5′ G-C-U-A-G-U 3′ Portion of DNA template 3′ C-G-A-T-C-A 5′ Associate with DNA synthesis: Complementary bases in mRNA 5′ G-C-U-A-G-U 3′ Change all U’s to T (no U in DNA) 5’ G-C-T-A-G-T 3’ Follow normal base-pairing rules: 3′ C-G-A-T-C-A 5′ Alshehri, Dikhnah Saeed EXERCISE 4 Answer the following: a) What codons specify tyrosine? b) What amino acid is coded by CCG? The ANSWER: a) Table (1) UAC and UAU. b) Table (2) Pro (proline). Alshehri, Dikhnah Saeed Alshehri, Dikhnah Saeed